FIG. 1 is a perspective view showing disassembled elements that are used at a conventional inkjet head device of an inkjet printer. In FIG. 1, the reference number 10 designates a lever, 13 a driving mechanism for driving the lever 10, 20 a carriage for mounting an inkjet head thereon, 21 an air releasing pin, 22 a negative pressure pin, 23 an elastic member, 30 a subtank mounted on the carriage 20 for holding ink, 31 an air releasing opening used for adjusting a pressure inside a subtank case to be an atmospheric pressure, 32 a negative pressure lever, 40 an inkjet head (hereinbelow, referred to as a head), 50 an ink cartridge, and 51 a connection tube for connecting the ink cartridge 50 to the subtank 30 to provide ink to the subtank 30.
In the case of an inkjet printer that includes the cartridge containing a large amount of ink, or an inkjet printer for producing high quality image, when the ink cartridge and the head are attached in the carriage together, the weight of the carriage can affect the operation the head so as to cause the image to be out of the correct position at the time the carriage 20 works. For this reason, as shown in FIG. 1, the ink cartridge 50 is disposed external to the carriage 20, and the subtank 30 that temporarily holds ink is mounted on the carriage 20.
When the inside pressure of the subtank 30 is positive, ink leaks (is exuded) from the head 40 due to the weight of the ink in the subtank 30. Accordingly, it is necessary to set the inside pressure of the subtank 30 to be negative. Such pressure setting becomes important when ink is ejected from the head. However, the ink can be mixed with air that enters the subtank 30 from the ink cartridge 50 or the connection tube 51. As a result, an amount of the air in the subtank 30 gradually increases, and thereby, the inside pressure of the subtank 30 changes so as to degrade the image formed by the ink. In order to deal with this problem, the ratio of the air inside the ink cartridge 50 as well as the inside pressure of the ink cartridge 50 are periodically controlled so as to become the original values.
FIG. 2 is a perspective view showing disassembled elements of the subtank 30. The subtank 30 includes a case 33 having an approximately rectangular upper wall 39a, an approximately rectangular bottom wall 39b, and three approximately rectangular side walls 39c. The case 33 has one open side. The subtank 30 further includes a film 34 for covering the one open side of the case 33, an elastic member 36 for pressing the film 34 from the inside of the case 33 via a plate 35, and a negative pressure lever 32 that is elastic and plate-shaped and presses the film 34 towards the inside of the case 33 from the outside of the case 33. The setting is made such that the force on the film 34 exerted from the inside by the elastic member 36 is larger than the force on the film 34 exerted from the outside by the negative lever 32. Accordingly, at the initial setting, the film 34 is pressed outwards. The balanced position of the film 34 determined by the negative pressure lever 32 and the elastic member 36 changes in accordance with the change in the inside pressure of the subtank 30 during the operation. When an amount of the ink in the subtank 30 decreases, the film 34 is pressed inwards, accompanying the change (reduction) of the inside pressure.
In a normal state, an air releasing opening 31 provided on one of the side walls 39c is sealed with an elastic member 311 such as a spring, a sphere 312, an elastic member 313 such as rubber, and a cap 314 that closely contact with one another. Also, in a normal state, an ink providing opening 37 provided on the upper wall 39a of the case 33 is sealed with an elastic member 371 such as a spring, a sphere 372, an elastic member 373 such as rubber, and a cap 374 that closely contact with one another. The spheres 312 and 372 are pressed by the elastic members 311 and 371, respectively. The ink providing opening 37 becomes open by the pressure of the ink that flows to the subtank 30 from the cartridge 50 via the connection tube 51 shown in FIG. 1, and thereby, the flowing ink is provided to the inside of the subtank 30. The air releasing opening 31 becomes open when the air releasing pin 21 provided on the carriage 20 shown in FIG. 1 is pressed inwards to adjust the inside pressure of the subtank 30.
The negative pressure pin 22 of the carriage 20 presses the negative pressure lever 32 of the subtank 30 inwards from the outside. That is, the negative pressure pin 22 is pressed inwards so that the negative pressure lever 32 can be moved towards the inside of the subtank 30, and the inside capacity of the subtank 30 can decrease. The elastic member 23 is provided for forcing the negative pressure lever 32 and the negative pressure pin 22 to be separated from each other. Therefore, in a normal state, the negative pressure lever 32 and the negative pressure pin 22 do not contact each other due to the elastic member 23.
In the operation of the inkjet head device having the above-described structure, the air releasing pin 21 is operated to open the air releasing opening 31, and the negative pressure pin 22 is operated to press the negative pressure lever 32 inward so that an inside capacity of the subtank 30 can become reduced. Then, in the state in which the subtank 30 has the reduced capacity, the subtank 30 is filled with ink via the ink providing opening 37. The filled ink is detected by filled ink detection sensors 38 disposed at the upper part of the subtank 30. Based on the result detected by the filled ink detection sensors 38, providing of the ink is controlled. In accordance with this control, the volumes of air and ink inside the subtank 30 are determined. Then, the air releasing opening 31 is closed. In the state in which the air releasing opening 31 is closed, the negative pressure lever 32 that is held at the inward position is released by removing the inward pressing force on the negative pressure lever 32. By performing such an operation, it is possible to control the inside pressure of the subtank 30 to be a constant negative pressure, and to stabilize ink ejection characteristics of the head 40.
FIG. 3 is a perspective view showing an example of the structure of a driving mechanism provided at the main body side of the printer for pressing and moving the negative pressure pin 22 and the air releasing pin 21. In FIG. 3, the reference number 10 designates a lever, 11 an air releasing pin pressing part, 12 a negative pressure pin pressing part, 14 a cam, 15 a solenoid, 16 an elastic member, 17 a sensor (HP sensor), and 18 a rotational shaft. The lever 10 includes the air releasing pin pressing part 11 for pressing the air releasing pin 21, and the negative pressure pin pressing part 12 for pressing the negative pressure pin 22. The pressing phase or level at which the air releasing pin pressing part 11 presses the air releasing pin 21 is different from the pressing phase or level at which the negative pressure pin pressing part 12 presses the negative pressure pin 22. With this difference in the pressing phase, when the lever 10 is operated, the air releasing opening 31 is made open by the air releasing opening pin 21 before the negative pressure lever 32 is pressed. Furthermore, with this difference in the pressing phase, after the air releasing pin 21 is moved outwards, and the air releasing opening 31 is thereby made closed, the pressing force acting on the negative pressure lever 32 by the negative pressure pin 22 is released.
The elastic member 16 drives the lever 10 to move in the direction opposite the direction of pressing the negative pressure pin 22 and the air releasing pin 21. The rotational shaft 18 to which the cam 14 is attached is provided for moving the lever 10 so as to perform the pressing operation of the negative pressure pin 22 and the air releasing pin 21. Accompanying the rotation of the rotational shaft 18, the cam 14 acts on the lever 10 so as to move (rotate) the lever 10. The solenoid 15 having a flapper is provided for rotating the rotational shaft 18. A filler provided on the rotational shaft 18 releases/shields the sensor 17 so that the sensor 17 can detect a home position (HP) of the rotational shaft 18.
The above-described ink filling operation in which the subtank 30 is filled with ink by pressing the negative pressure pin 22 and the air releasing pin 21 is referred to as an air releasing filling operation. In the air releasing filling operation, it is possible to keep a pressure in the subtank 30, an amount of the ink in the subtank 30, and an amount of the air in the subtank 20 at desired values. On the other hand, an ink filling operation in which only ink is provided to the subtank 30 without pressing the negative pressure pin 22 and the air releasing pin 21 is referred to as a normal filling operation. In the normal filling operation, the air amount in the subtank 30 that has gradually increased is not controlled, so that the inside pressure of the subtank 30 is shifted from a desired value.
FIG. 4 is a partial schematic illustration for a lever operation mechanism provided at the main body of the printer. In the above-described structure, in order to press and move the negative pressure pin 22 and the air releasing pin 21, it is necessary to apply a force to the lever 10 that is larger than the reaction force by the negative pressure pin 22 and the air releasing pin 21. As shown in FIG. 4, in the conventional structure of the cam 14, the lever 10 is rotated counterclockwise by the cam 14, the cam 14 being rotated clockwise by the rotational shaft 18. Accordingly, the reaction force R1 by the lever 10 acts on the rotational shaft 18 to apply a rotational force R2 that drives the cam 14 to rotate in the direction opposite the desired operation direction. For this reason, in order to rotate the cam 14 to move the lever 10, a motor or a solenoid that has a high driving force is conventionally used as a driving mechanism at the main body of the printer for operating the lever 10.
However, the air releasing filling operation needs to be performed only when the air amount inside the subtank 30 increases, and in reality, the necessary frequency of the air releasing filling operation is much smaller than that of the normal filling operation. Accordingly, in terms of the manufacturing costs of the printer, it is not wise to use the expensive motor or solenoid for the air releasing filling operation having the less necessary frequency.
FIGS. 5A, 5B, and 5C are illustrations for the lever operation at the carriage on which plural-color subtanks are mounted. The order of the lever operation procedure is from FIG. 5A to FIG. 5C. In FIGS. 5A through 5C, the subtanks (not shown) that correspond to a plurality of colors (in this example, four colors) are provided on the carriage 20. In the drawings, air releasing pins 21a through 21d, and negative pressure pins 22a through 22d that correspond to the respective subtanks extend from the carriage 20. For example, in the case of tying to press the air releasing pin 21a and the negative pressure pin 22a located at the most left side of the carriage 20 when seen from the pin side to perform the air releasing filling operation, the air releasing pins 21b through 21d and the negative pressure pins 22b through 22d of the other subtanks corresponding to the pins 21b through 21d and pins 22b through 22d are also successively pressed by the lever 10, accompanying the movement of the carriage 20. When these affected other subtanks are not filled with the ink, the air amounts in the subtanks become larger than in the case where the appropriate air releasing filling operation is performed. Furthermore, in this case, the inside pressures of the suntanks cannot be controlled to be a desired value.
Furthermore, in the related art, generally, an inkjet printing apparatus is applied to an image printing apparatus or an image forming apparatus such as a printer, a facsimile machine, a copying machine, and a plotter. A printing head of the inkjet printing apparatus includes a nozzle for ejecting ink, a ejection room (a pressure room, a pressurized liquid room, or an ink passage) that communicates with the nozzle, and energy generation means for generating energy that is used for pressurizing the ink in the ejection room. When an image is recorded on paper by a serial printer, a carriage is moved in a main running direction, paper is fed in a sub-running direction, and the ink is ejected from the printing head. Instead of paper, any medium on which the ink will adhere may be used.
In such a serial inkjet printing apparatus, ink needs to be provided to the printing head mounted on the carriage. Generally, the printing head and an ink cartridge (or an ink tank) that provides ink are disposed together on the carriage. The ink cartridge integrally formed with the printing head may be disposed on the carriage.
An appropriate ink meniscus needs to be formed at the nozzle hole of the head when such an ink cartridge is used. Furthermore, it is necessary to prevent bubbles or foam from being formed. In addition, when the head is disposed so as to, be oriented in the downward direction, the ink needs to be prevented from dropping and leaking from the nozzle. For these reasons, the ink pressure needs to be negative. Accordingly, an inkjet printing apparatus that has a porous ink absorption body for absorbing the ink and that generates a negative pressure is widely used.
In another usage example, a subtank having a small capacity is disposed on the carriage, and a main cartridge having a large capacity is disposed at the main body side of the printer. In this arrangement, the ink is supplied to the subtank from the main cartridge disposed at the main body side.
In the case where the only ink cartridge is disposed on the carriage without using the main cartridge at the main body side, the ink cartridge needs to be replaced with new one when the ink cartridge runs out of the ink. Accordingly, when the ink is frequently used for high speed printing or high quality image printing, the cartridge needs to be replaced more frequently. On the other hand, when the capacity of the ink cartridge is made large, the weight of the entire carriage becomes large. Accordingly, it becomes difficult to move the carriage at a high speed, and further, the size of the carriage and the like becomes large. In addition to that, the output energy of the motor for driving the carriage needs to be large. Moreover, the weight of the carriage changes significantly, so that the movement characteristics of the carriage change during the printing operation, and it becomes difficult to maintain stable printing accuracy.
According to Japanese Laid-Open Patent Application Nos. 10-128992 and 10-235892, a subtank having a small capacity is disposed on the carriage, and the main cartridge having a large capacity is disposed at the main body side of the printer. The subtank is connected to the main cartridge by a tube. With this structure, when the ink in the subtank decreases, the ink is supplied to the subtank from the main cartridge. Further, according to Japanese Patent No. 3053017, two tubes, i.e., an ink providing tube and an air sucking tube are connected to the suntank.
In the above-described ink cartridge, the ink in the cartridge is sucked via the nozzle so that the negative pressure can be generated. The generated negative pressure is maintained by the porous body. However, the ink is wasted without being used, and the absorbing body for holding the waste ink in the printer becomes larger. In addition, using the only ink cartridge disposed on the carriage causes the ink shortage more often.
In the case of the printer disclosed in the above Japanese Laid-Open Patent Application Nos. 10-128992 and 10-235892, since the tube has permeability of air and moisture, the air enters the inside of the tube. Also when the ink supply unit is attached or detached, the air enters the inside of the tube. Since the disclosed printers do not have a function of discharging the air mixed with the ink inside the ink supply passage (the tube), a large amount of air enters the subtank when the tube is used for a long time, resulting in printing being degraded.
Furthermore, in the printer disclosed in the above Japanese Patent No. 3053017, the ink is provided to the subtank while the air is discharged from the subtank. Accordingly, the air is not accumulated in the subtank. However, in this printer, it is necessary to connect two tubes, that is, the ink providing tube and the air sucking tube to the subtank. Particularly, in the case of the color inkjet printing apparatus, eight tubes need to be connected to respective subtanks corresponding to four colors.
In this case, the subtanks are moved with the subtank being disposed on the carriage, the tubes connected to the subtanks need to have lengths that are at least equal to the length of the movement of the subtanks. Accordingly, it is necessary to arrange the plural long tubes in the printer, and to provide a special pump for generating the negative pressure, resulting in high manufacturing costs.